A flat panel display device has many advantages, such as thin body, power saving and no radiation, etc., and has been widely applied. Current flat panel display devices mainly include a Liquid Crystal Display (LCD) and an Organic Light Emitting Display (OLED). A Thin Film Transistor (TFT) is an important constituent part of the flat panel display device, may be formed on a glass substrate or a plastic substrate and is generally used as a switch device and a driving device to be applied to an LCD and an OLED.
A polycrystalline silicon (Poly-Si) thin film is formed by many small grains having different sizes and different crystal orientations, the sizes of the grains are generally from tens to hundreds of nanometers, and the sizes of large grains may reach several micrometers. A polycrystalline silicon thin film having large grains has a comparatively high mobility which is close to the mobility of a bulk material, thus, the polycrystalline silicon thin film has been widely applied to the manufacturing of a semiconductor component. For example, a thin film transistor in an LCD or OLED product is most adopted with a polycrystalline silicon thin film as an active layer.
The current manufacturing method of a polycrystalline silicon thin film mainly includes manufacturing an amorphous silicon thin film first and then performing a crystallization process on the amorphous silicon thin film to obtain a polycrystalline silicon thin film. Wherein Excimer Laser Anneal (ELA) is a commonly used method, which mainly performs a laser irradiation to an amorphous silicon thin film through an excimer laser having a certain amount of energy and enables the amorphous silicon to be transformed into a polycrystalline silicon at high temperature using the energy of the excimer laser. During a process of transforming an amorphous silicon to a polycrystalline silicon at high temperature using the ELA method, variant bumps are inevitably generated on a surface of the obtained polycrystalline silicon thin film, and have an impact on subsequent manufacturing processes and finally on stability of an electrical performance of a thin film transistor to reduce quality of a product.